Musannaf Ibn Abi Shayba 36:537

Waki’ narrated to us, from Isma’il bin Abi Khalid, from Hasan bin Muhammad, who said: Umar said to Uthman: "Fear Allah, and if you are put in charge of any of the affairs of the people, do not place the sons of Abi Mu’ayt upon the necks of the people." And he said to Ali: "Fear Allah, and if you are put in charge of any of the affairs of the people, do not place the sons of Hashim upon the necks of the people."